


Something's Fishy

by ClapAlienCheex



Category: Invader Zim
Genre: Adventure & Romance, Eventual Smut, Fluff and Humor, M/M, ZaDr, mermaid au
Language: English
Status: In-Progress
Published: 2020-06-04
Updated: 2020-06-06
Packaged: 2021-03-04 03:34:16
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings, No Archive Warnings Apply
Chapters: 3
Words: 4,456
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24537055
Author URL: https://archiveofourown.org/users/ClapAlienCheex/pseuds/ClapAlienCheex
Summary: Based on shandzii's 'Invader Zim' Mermaid AUZim has been assigned to infiltrate the land walkers' territory in hopes to conquer it for the Merkin Empire by Biggest Red and Biggest Purple, unaware that his mission is nothing more than his exile. On the surface, he meets a paranormal investigator named Dib. The two butt heads, but over time their relationship begins to blossom into something more.
Relationships: Dib & Zim (Invader Zim), Dib/Zim (Invader Zim)
Comments: 7
Kudos: 91





	1. Surfing Will Scare Them Off

**Author's Note:**

> Go follow shandzii on Tumblr, their artwork is awesome!
> 
> More chapters coming soon!

“My Biggest, Miyuki!” Zim chirped as he eagerly swam up to the giant mermaid. Her eyes sparkled blue as she looked at the small merboy. “I have unleashed a giant monster to take care of those filthy land creatures!”  
“What?!” she shrieked. “No, Zim, send it back!” She quickly swam away but it was too late. The even larger squid monster caught her in its tentacles, taking her with it.  
“Oh… That can’t be good.” Zim muttered to himself. Another large Irken came to the scene, startled to see that his mate was gone.  
“Zim?” Spork asked as he looked everywhere. “Where’s Miyuki?” The smaller merboy pointed almost innocently towards the direction of the squid monster. His eyes widened when he saw the beast. “What did you do?!”  
“I unleashed it to get rid of the land creatures, duh!”  
Spork groaned, glaring at the small Merken. “When I get back from saving Miyuki, you’re going back to the Smeetery!” Spork swam off, and Zim waited, but they both knew that neither of the larger Merkens would be returning.  
….  
Zim swam with his school, looking around and noticed how much smaller he was compared to most of them. Sure, Bob was the smallest—thank Merk for Bob—but even Stoodge, who had been by Zim’s side since the Smeetery, was getting bigger… At least he’s ugly and I’m beautiful, he thought to himself.  
The large group swam up to a clearing where Red and Purple were in the middle of. “Fellow Merk kind!” Red cried out. “It was only mere weeks ago that our Biggests, Miyuki and Spork, had gone missing after someone released the Kraken monster.” Everyone’s eyes quickly turned to glare at Zim. Before he could defend himself, Purple interjected.  
“As tragic as their disappearance is,” he sighed. “The Control Shell have decided that it’s time that our society moves on and claim new Biggests. Isn’t that right, Control Shell?” The audience turned to a giant, unmoving shell. It didn’t say anything. It never did—at least not to the smaller Merkens; they are unworthy to hear its wisdom.  
“The Control Shell,” Red said. “Has declared Purple and myself as your next Biggests! Good for you. To celebrate, we have decided to expand our empire! We are the most superior species in the entire world, and the rest of the creatures need to learn that.”  
“Some of you are going to be tasked with invading tribes and other societies,” Purple informed. “You will go in, learn their weaknesses, and try to see if they will join us willingly. If not, well, we’ll get to that when the time comes.”  
“We do have one special task, however,” Red announced, making his way towards the crowd. “There is the matter of the land creatures. We need one of you to go up there and, I don’t know, keep them out of our business or something.” The Irkens looked at each other, all afraid of the mission. “Do not fear, one lucky Irken has already been—”  
“ME!!”  
Everyone turned to see Zim yelling from the back of the crowd, waving around his webbed claws frantically. “Pick me!! I am Zim!! I am the worthiest Irken for this mission!!”  
“Please, slither forward, Zim,” Purple commanded. Zim obliged and swam up to the two. “What a coincidence that you would volunteer because we have decided to send you.”  
The small merboy gasped, his magenta eyes sparkled. “Really?!”  
“Yes, yes,” Red said to him. “Now, you don’t have much time. Their hot star will be gone soon, and you need to get up there, like, right now!”  
“Yes, My Biggest!” Zim saluted. “Oh, can I get a fish slave?”  
The Biggests looked over at their shark cage full of red-eyed fish slaves then noticed one that had blue eyes and markings that kept swimming in and out of the cage. “Yeah, you can have that blue one.”  
Zim looked over and saw what it was doing. “Um… Is it supposed to be stupid?”  
“It’s not stupid,” Purple informed. “It’s advanced!”  
“Well, Zim,” Red interjected. “You better get going!”  
“Thank you for this special mission, My Biggests!” Zim saluted and swam over to the weird blue fish. “You! You are now my fish slave. You will be accompanying me on my mission to infiltrate and ultimately destroy the filthy land walkers. Now, do you have a name?”  
The blue fish got serious and met his new master. “Gir, reporting for duty!”  
“Okay, Gir, let’s go!” Before they started swimming, the blue fish started screaming. Zim stared at it, concern washing over his face. Upon realizing that the fish wasn’t going to tire itself out, its master had no choice but to step in. “Gir!” The fish stopped its screaming and the two started swimming away from their school.  
______

Dib stared out at the ocean, his feet buried in the sand, enjoying the cool texture on his toes. His knees were tucked under his chin and it looked like he could doze off at any moment.  
“You’re still out here?” a voice asked.  
Dib whipped his head around to find Gaz staring down at him. Her short hair was damp, and her wetsuit was slowly drying off. “Yes, Gaz, I’m still out here,” he sneered. “No thanks to you. You know surfing will scare them off!”  
Gaz rolled her eyes and placed her surfboard down before sitting down next to her brother. “Don’t you think dad would tell us if there were mermaids, Dib?”  
The brother made a dry laugh. “Yeah, right. He could be looking at a mermaid and say they’re not real right to her face.”  
“Whatever. But it’s getting late and I’m leaving—I’m meeting up with some friends for drinks. Try to get home before the morning.”  
“Yeah, yeah, go have fun. And when you see me, I’ll have proof!” Dib gave a mischievous grin as he held up his camera.  
“Why do you even have that old piece of junk anyway? Just use your phone like everyone else?”  
“What, so I can let the photo guys at the drug store laugh at me when I get the photos printed? Uh, no thanks.”  
Gaz rolled her eyes, got up with her surfboard, and started walking away, mumbling something that Dib couldn’t hear.  
Hours had gone by and the sun had set. Dib hadn’t even realized he fell asleep until he was woken up by something screaming. His head whipped around, but no one else was on the beach. He stood up to get a better look when he noticed some splashing in the water. “Holy shit—hang on!” He threw off his shirt and quickly jumped into the water. It only took a few seconds for him to feel a small figure, their arms thrashing a bit, but their voice was muffled by the water. Dib wrapped his arms around their frame and quickly pulled the both of them up to the surface. “Hey! Are you o—”  
Dib’s eyes widened as he looked at the person he just saved, but it wasn’t a person. This creature had green skin, magenta eyes, and some kind of antenna.  
A mermaid.


	2. Mermaids Are Green?

Zim and Gir had been swimming for hours. Eventually, the two made it to the surface. “Okay, Gir, be quiet, I’m going to take a look to make sure that no land walker is around.” The fish got a serious look on his face and gave a nod. The Merkin poked his head out of the water, scanning the sands for any humans. Eventually, his eyes fell on a human. Before he could react, he realized that the human didn’t see him. “Gir, I’m going to go in a little closer. Stand guard!”  
“Yes, sir!”  
Zim started swimming closer to the land, never taking his eyes off the human. ‘It’s… sleeping,’ he thought to himself. Before he could inspect the land walker, he heard Gir making a commotion. He got under the water and looked around to find Gir screaming at a hermit crab. “Gir! You’re going to blow our cover!!”  
“This shrimp is homeless!!” Gir cried before he started screaming again.   
Zim was about to stop his fish from creating a bigger scene, but it was too late. Before he could do anything, something jumped in the water. Zim looked and it was the sleeping human, except it had exposed its underbelly. For a moment, it looked like it couldn’t see him, and Zim almost felt relieved, until the human wrapped its big, strong arms around him, pulling the both of them up to the surface.  
“Unhand me, you filthy land walker!!” the green thing screeched, thrashing around in Dib’s arms. “You dare touch an almighty Merkin?!” The thing glared at him, its antenna pressed against its head, like a feral cat.   
Dib quickly pulled his hands away, but he kept staring. “A-Are you a mermaid?”  
“A what?” The green creature gave him a confused look. “Is that what you disgusting beasts call us?”  
“Well, what should we call you?”  
“We are the great and powerful Merkins!”   
Dib tried to stifle his laugh but couldn’t hold back. “Hold on—your species are called Merkins?!” At this point he had tears in his eyes.   
“So?!”   
“That’s what we call pubic wigs!!”  
Zim looked confused. “What does that mean?”  
Dib’s laughter stopped almost abruptly. “Oh… Yeah, you probably wouldn’t get why that’s funny… Would you?” He sighed and looked over at the beach, shivering as he noticed just how cold the water was. “Hey, uh, are you able to get on land? I didn’t realize how cold it is.”   
The mer critter looked over at the land and felt nervous. “I’m not sure…”   
The human held out his hand. “Tell you what, if you can’t, I’ll put you back in here.”   
Zim nervously took the land walker’s hand, swimming behind him, Gir following along. Just as they were about to get out of the water, the Merken pulled back. “I-I can’t…” His magenta orbs scanned the land now that he was a little closer.  
“That’s fine, maybe another time?” Dib grabbed his discarded shirt and glasses and pulled it on. “Hey, can I get a picture?”  
“What’s a picture?”  
“Jesus fucking Christ,” he said as he pinched the bridge of his nose. “Y’know what—I’m just gonna…” Just as he was about to grab his camera, Zim used his tail to splash some water on the device. “My camera!!” He glared at the mermaid. “Why did you do that?!”  
“No one will be getting a picture!! What do you intend on doing with that technology? Reveal me to the world?!” Zim growled, exposing his sharp teeth. “My kind are familiar with you land walkers, always trying to expose us…”  
“Ugh, you’re such a dick,” Dib grumbled, inspecting his camera. ‘At least I have my phone,’ he thought to himself, his hand guiding to his wet pocket. “Oh—son of a bitch!”   
“Ha! My plan to destroy your technology has been a success!! Praise me!!”  
“Fuck you, man!”  
“Fuck me yourself, you coward!!”  
Dib blushed, his eye started twitching. “Oh my god, please, never say that again..!”  
“I will say whatever I feel like saying, land beast,” Zim grinned. “Now begone with you!”  
The human groaned, collecting his damaged goods. “Hey… You gonna be here for long?”  
“Uh, I don’t know,” Zim said as he looked around. “However long it takes for me to complete my mission.”  
Dib perked up at that. “Mission? What mission?” He asked as he stepped back into the water.   
“Fool! That is top secret Merken information!” Zim crossed his arms. “I will, however, still be here when your hot star rises….”  
Dib couldn’t help but smile a little bit. “Hey, uh, I’m Dib.”  
“Zim.”  
______

Dib woke up the next morning—or, afternoon—eager to head to the beach. He rushed downstairs to grab a bowl of cereal, grinning ear to ear as he greeted his family. “Good morning, dad, Gaz!” He said in a chipper tone, much to Gaz’s annoyance.   
“Ugh, Dib, it’s too early for this bullshit,” she groaned.   
“I’m just in a good mood!” he defended.   
“Is that so, son?” Dib’s father, world famous Professor Membrane, asked. “What’s got you so chipper this fine morning?”  
“I met someone last night,” Dib responded with a cheeky grin.   
“Gross,” Gaz mumbled.   
“No, it’s not like that,” he sighed. “Well, last night, I dozed off on the beach, and I woke up to screaming! I jumped into the water and I found a mermaid!!”  
“Oh, not this again,” Professor Membrane pouted. “My poor, insane son… There are no such things as mermaids!”  
“Yes, there are! Although, they don’t look like I thought they would…”  
“What do they look like?” Gaz asked.   
“Funny enough, they kinda look like those goofy aliens from cheesy sci-fi movies. Y’know, green, big eyes, no nose or ears, but with a fish tail.”  
“Mermaids are green?” was all Gaz had to say as she grabbed her Nintendo Switch. “Well, I’m hungover, and I’m done with this conversation.”  
Professor Membrane looked at Dib, a look of concern peering behind his thick goggles. “Look, son, you are a marine biologist—which I’m very proud of—but you need to focus on your job and stop trying to go after these paranormal things!”  
“I wasn’t even investigating anything,” he lied. “Can’t a man just relax on the beach all day?”  
“Son, I want to believe you,” Membrane said as he sat down across from his son, cupping his tea between his gloved hands. “But without any proof, it’s just a bunch of Bologna.”  
“Bologna?!”   
“Perhaps if you had some proof…” his voice trailed off.  
“Well, I would, but that stupid mermaid ruined my camera,” Dib grumbled, but then a thought popped into his head. “Hey, wait, dad—you could come with me to the beach!! I’m sure the mermaid is still there!”  
“Oh, I can’t son. I have a conference to get to in Hawaii. I’m waiting for my cab to pick me up.”  
“Why didn’t you ask me to take you?” Dib asked, a little hurt, but mostly annoyed.   
“I hadn’t thought to ask.” Before their conversation could continue, a car pulled up and honked its horn thrice. “Looks like my ride’s here. You two take care of yourselves and, if you want, I’m supposed to get back at 11:00 in the evening next Saturday. Let me know by Wednesday if you’re able to pick me up.” Membrane got up and started heading towards the door, Dib following behind.  
The younger Membrane noticed the luggage by the front door. “I’ll let you know,” he said with a smile. “Have fun, I love you.”  
“I love you, too, son.”  
______

Zim had perched himself on a boarder near the pier, splashing the water around with his tail fin. His eyes scanned the area, ensuring that no humans were around.   
Gir swam around him in circles for hours. “What we doing today?!” he asked with a giddy voice.   
“Oh, I don’t know,” Zim said absentmindedly. “Infiltrating the humans, conquering their world, blah blah blah.”  
“Ooooh!!”   
“Yes, I know, I’m so brilliant!” His eyes looked down at his fish slave only to realize Gir was referring to a shiny bug that was flying by. “Gir!” he snapped as the fish started swimming away, following said bug. The mermaid groaned and laid himself back on the rock, his fin still dipped in the water. “Ugh, whatever.”  
‘Why did My Biggests even send me up here?’ Zim asked himself as he stared at the blue sky and its weird puffy things. ‘I can’t even have my fin out of the water without having trouble breathing.’ With a sigh, the Merken lowered himself back into the water, feeling better as his gills breathed it in.   
“Aww what’s wrong?” Gir asked, rubbing his nubby fin along Zim’s face.   
“I dunno,” Zim shrugged. “This mission just doesn’t make much sense. I mean, as much as I hate these disgusting land walkers, I don’t see any reason why we should take over their world. I mean, it’s not like we can walk like that Dib-human, I can’t even have my fin out of the water, Gir! How exactly am I supposed to take over when I can’t even breathe?!”   
“I don’t know,” Gir said flatly, then he started laughing maniacally.   
“I know I shouldn’t be questioning My Almighty Biggests, but some things don’t quite line up!” Zim peered over at his fish-slave companion who was swimming around in circles, clearly trying to catch his own tailfin. “Gir! I will be swimming around the surface. I’m waiting for the Dib to show up. I think he is my key to figuring out how I can take over his kind.”  
Zim swam up and, almost as if he had been summoned like the Great Cthulu, Dib was quickly making his way to the water. When he spotted Zim, he got a big smile on his face and waved. “Hey, Zim!” Dib said as he approached the Merken. “Thanks for not taking off, I was hoping to get to ask you a few things. That is if it’s okay,” he added, sheepishly.   
“Yes, yes, that’s fine, Dib-stink,” Zim said with a cocky grin. “You may ask the great Zim anything you like on the condition that I do the same.”   
“Wait, you wanna interview me?” Dib asked stunned. “What’s so interesting about me?”  
“You’re a human, and I would like to learn a little bit about the creatures I’m supposed to conquer, y’know, to figure out your weaknesses and stuff.”  
“Oh, yeah, that makes sense—wait! I’m not gonna tell you our weaknesses!”  
“Then you may not ask me anything!!” Zim screeched.   
Dib took a deep breath and smiled at the water dweller. “Alright, you win, Zim. I’ll tell you anything you’d like.”  
“That’s more like it! The deal is back on.”  
_____

“How old are you?” Dib asked as he laid on the rock.   
“In Merken years, I’m 200,” Zim replied. “I don’t know how old I’d be in human terms. How old are you?”  
“In human years, I’m 24, almost 25.”  
“Your birth anniversary approaches?”   
“Yep! June 9th.”  
“What’s June?”  
“It’s a month up here—it’s June 5th now.”  
“Are you looking forward to your first quarter?”  
“My what?” Dib asked as he sat up to look at the Merken, chuckling.   
“Merkens celebrate every quarter we exist,” Zim informed nonchalantly. “Like I said, I am 200, so I have had eight quarters.”   
“Huh, sounds like fun,” Dib mused. “Most humans only get up to three, very few get to four.”  
“Do your people not live long?”  
“Well, we do, compared to animals—except for some turtles, those guys live forever—but no one would ever live to be 200 years old.”  
“That’s stupid.”  
“I know!”  
“What are humans like?” Zim asked, uncharacteristically nervous. “Are they like you?”  
“I mean, some, I guess,” Dib said with a sigh. “But everyone is different. I don’t really know how to explain it without having to explain every little thing.” He eyed the Merken, noticing his gills along where his ribs would be. “Did you find out if you can breathe outside of water?”  
“I tried earlier, but I almost suffocated. I had to dip my tail fin in the water, but that left my Glorlox feeling dry.”  
“What’s a Glorlox?”  
“It’s my breathing tube.”  
“Oh, humans have something similar.”  
“What’s your breathing tube called?”  
“Trachea.”  
“Sounds gross.”  
“It’s probably our least-grossest organ.”  
“What’s your grossest?”  
“The small intestine. Despite its name, it’s 20 feet long.”  
“Is that big?”  
“Well,” Dib jumped down to show how tall he was. “I’m a little over six feet tall.”  
“Oh, Merk,” Zim said with a blush, scanning the human. He hadn’t realized how tall he was before but seeing him up close in the daylight revealed that he was a tall specimen. “You’re about the size of My Biggests.”  
“Your Biggests?”  
“Yes, they are our leaders.”  
“Wait, your leaders are just bigger than everyone else?”  
“That’s right.”


	3. You Got Pink Duck Legs

A few days had gone by since Dib met the curious green mermaid. The two had talked every day, getting to learn a little more about each other’s culture. Dib learned about the Control Shell and how it only spoke to Merken elite. Zim found out that his kind are referred to as ‘mermaids’ and depicted as half human.   
“Of course your kind would interject yourselves onto us,” Zim said smugly. “We are amazing, and anyone would be lucky to be around us. You should feel honored I give you the time of day~”  
“Hey, if I remember correctly,” Dib said as he took a bite of his sandwich. “You’re the one who was really excited to see me this morning.”   
“You lie!” Zim screeched. “You lieeee!!!!”   
“Easy man,” Dib laughed. “You’re gonna make me choke!”  
Dib wiped a tear away from his eye with his thumb. Zim couldn’t help but stare at him. “Curious. Your eyes leak. Why is that?”  
“Huh? Oh… Well, I was laughing, and sometimes that can trigger tears. Humans usually cry as an involuntary reaction from emotions and things like sneezing, pain, and, I don’t know, some other stuff.”  
“Weird.”  
“Yeah, it is pretty weird,” Dib scarfed down the rest of his sandwich and took a sip of his Poop-Cola. “Hey, I was working for the past couple of days on making something that I think will help you breathe on land.”  
“Is that so, Dib-filth?”  
“Yeah, here,” he reached into a bag he had next to him and pulled out a pack that had two tubes, one on each side. Upon closer examination, Zim could see that it contained water and had three pink circles on it. “I call it a PAK, stands for Procured Aqua Kit. So, this is, basically, a filtration system. These tubes connect to your gills and the water will be pumped in and out and you should be able to breathe properly. Now, I don’t have any DNA samples to know what needs to be filtered out so it’ll just be pumped in and out of your gills for right now. Maybe later on I can collect some samples and figure out how to make it more efficient.” The human took off his socks and shoes and waddled into the water. “Here, let me help you put it on.”  
Zim lifted his arms timidly, just enough to reveal his gills better. “I-Is it going to hurt?”  
“Well, I did everything I could to make it comfortable,” Dib started. “However, I can’t confirm nor deny if it’ll hurt. Just to relax, okay?” He gave Zim a soft smile and the Merken felt his heart beating against his chest. Dib connected the tubes to Zim’s gills carefully, glancing at him once in a while to check for any signs of discomfort. “If anything hurts, just let me know, okay?”   
Zim nodded his head, but the truth was it didn’t hurt at all. It mostly felt weird, but once it was on, it was working like a charm. “Incredible, Dib-beast! This fits me quite well!”  
“I’m glad to hear it!” He smiled a big, goofy grin then offered both of his hands. “Okay, now, let’s do the next step.”  
“There’s more?!”  
“Well, yeah. I made this so that you could breathe on land and, well, I wanna see if you can get out of the water.”   
That made the Merken tense up. “O-Okay…” his voice trembled. The two slowly edged their way onto the beach. Before he could crawl himself out of the shallow, Dib pulled the fish into his arms and carried him bridal style. “What are you doing?!” Zim blushed as he wrapped his delicate arms around the human’s neck.  
“I’m carrying you, silly,” Dib mused. “I wasn’t gonna make you crawl around.”  
“Oh…” Zim noticed just how much bigger the human was compared to him. His heart started beating more. “Thank you.”   
“Did you just thank me?”   
“I swear to Merk I will—” Before Zim could finish his sentence, Dib gently put him down on the sand. “Oh! This isn’t so ba—” His words were cut off by his terrible screaming. Dib flinched then noticed what was happening. He took out his phone and started to discreetly film Zim’s transformation. The Merken’s tail was melting away and leaving behind a pair of pink, scaly, duck-like feet. Zim sat there whimpering, clumps of his melted tail gooped around him.   
“Holy fucking shit, dude,” Dib rushed over the mermaid and knelt beside him. “Are you okay?!”   
Zim looked up at the human, tears forming in his eyes. “I-I think I understand what you mean by tears being produced from pain.”   
Dib examined the Merken’s new legs. “Ha! You got pink duck legs!” His eyes went up the scaly limbs and then he adverted his gaze when as he realized he’d be looking at a naked Zim. “I should, uh, probably have gotten you something to wear…”  
“What do you mean by ‘something to wear?’”  
“Y’know, cl—oh, you probably don’t know.” Dib sighed and took off his shirt. Zim looked over the creature and noticed he had some patches of hair.   
“What’s that on your chest and stomach?” He asked pointing to the patches.   
“Oh, that’s just some body hair?”  
“And what is this hair nonsense of which you speak?”  
“You see the black stuff on top of my head?”  
Zim looked up at his big cowlick. “Yes.”  
“Okay, that’s hair, and most humans have it all over. Most of it is usually on the top of our heads, and for some of us, we get a little bit on our bodies, like on our chest, stomach, limbs, and, uh, some other areas.” Dib tossed Zim his tee shirt. “Okay, this might be a little big, but it’ll cover you. I live right next door so we shouldn’t worry about people seeing you.”  
Zim stared at the discarded shirt in his hands. His antennae vibrated and moved to inspect the article. His heart started to beat again, and his blush returned. ‘This is the human’s scent…’ Zim wasted no time in putting the shirt on, but it did take a few tries for him to get it on properly. The first time he put his head through the arm hole. The second time he tried pulling it on using the head hole, and then the third time he had his head go through the other arm hole. Eventually, he got it on backwards and inside out, but Dib was just happy that he was covered up.   
‘This fish is gonna be the death of me.’


End file.
